My 2020 Rad Rover ST has a little over 4,000 gentle miles on it. I've replaced the chain once and both clean and lube fairly often. I have the tool to measure chain wear so know when I need a new chain. As far as I can tell though there is no way to measure cassette wear. I watched a couple of videos with things to look for which are a little helpful but also heard things like: "If you put on a new chain and there is still skip you need a new cassette." Would prefer NOT to have that happen. So, in general, how many relatively gentle miles should I expect to get from a cassette and, again in general, do you replace both the cassette and the chainring at the same time?